Group B meningococcal capsular polysaccharide (GBPS) consists of a linear polymer of alpha (2->8) linked N-acetyl neuraminic acid. Immune response to GBPS in humans has not been studied in detail. Most of the assays in use modify the structure of native antigen or its conformation to varying extent. We adopted an ELISA to measure antibodies to both GBPS and Escherichia coli K1, 0-acetylated polysaccharide in sera of healthy normals and group B meningococcal patients and carriers. In general, non-carriers showed higher total immunoglobulin levels to 0-acetylated K1 CPS than to GBPS, whereas patients and carriers had more antibodies to GBPS. Both IgG and IgM capsular antibodies were found. Attempts are under way to standardize ELISA to quantitate antibodies and express results in an acceptable unitage. Both the coating antigens are being used in different forms to understand finer epitope specificities. We intend to investigate possible association of various epitopes with different biologic properties. The kinetics of antibodies induced in laboratory animals by GBPS conjugates with and without adjuvants are being studied.